This application is based upon application No. 11-206088 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a detecting device and a camera having the detecting device.
2. Description of the Related Arts
Conventionally, there have been known some focus detecting devices, applied to cameras for example, which have lenses forming respective subject images by focusing beams of light coming from a subject and detect a focus or a distance from the subject, based on difference between the subject images.
Many of the focus detecting devices use line photo acceptance units having one-dimensional array or line, that is to say line sensors, which are of the charge accumulation type, and operate a shift of the focus or the distance, based on the difference of the subject images, which change in a arranging direction of the photo acceptance units corresponding to the distance from the subject.
As to the focus detecting devices, which use the photo acceptance units having one-dimensional array or line, however, the detecting region thereof is limited by the position and size of the subject. Therefore, in order to improve this problem, a method, which uses photo acceptance units, having two-dimensional array or matrix and being of the charge accumulation type, so as to detect the subject in the wide range, has been proposed (for example, U.S. Pat. No. 5,815,742).
As for general photo acceptance units, having two-dimensional array or matrix and being of the charge accumulation type, the charge accumulating time thereof is set a predetermined period at first. The data of charge thereof is read, and then the charge accumulating time is adjusted suitably, depending on the read data. Namely, the charge accumulating time is made shorter when the read data is overflowed, and the charge accumulating time is made longer when the read data is less than the desired level. Thereafter, the data are read again. The above procedures may be repeated, if the brightness of the subject is excessively high or low.
Thus, this method is not suitable for the focus detection which needs the rapid processing.
So, the method for controlling the charge accumulating time in real time by monitoring the brightness of the subject with a monitor arranged around the units has been proposed (for example, Japanese Non-examined Patent Publication No. 10-126681).
In the case of arranging the monitor around the area sensor, the charge accumulating time can be set suitably, when the brightness of the subject is uniform. When the brightness of the subject is not uniform, however, necessary data may overflow or be less than the desired level, and thus the focus can be detected with no accuracy.
It is not an especial case that the brightness of the subject is not uniform, and this may happen about the very usual subject. For example, in photographing a person, there is the case that the image of a portion of his or her clothes is made upon a monitor arranged around the area sensor, and the image of a portion of his or her face is made upon the area sensor. In this case, if the charge accumulating time is controlled depending on the data monitored by the monitor, the charge accumulating time becomes longer or shorter than the suitable one for the sensor, which senses brighter or darker portion than another portion monitored by the monitor. A difference in luminosity between the clothes and the face of the person may sometime exceed over three steps of diaphragm stop, which is equal to 8 times differences in accumulating time and data size. This causes a detection error.
Accordingly, it is an object of the present invention to provide a detecting device in which the detecting error is reduced even if the brightness distribution of the subject is not uniform. It is another object of the present invention to provide a camera having the detecting device.
In order to achieve one of the above objects, according to one aspect of the present invention, there is provided a detecting device for detecting one of a focusing condition and a distance from a subject, comprising: optical members which form respective subject images on respectively individual positions; area photo acceptance units, which are of a charge accumulation type, arranged on the respectively individual positions focused by the optical members; and at least one of brightness monitoring photo acceptance units, arranged across a detecting area of at least one of the area photo acceptance units, for controlling charge accumulating time of the area photo acceptance units.
The detecting device can be used, for example, in a single-lens reflex (SLR) camera in order to adjust the focus position of a photographic lens based on deference in the image forming positions (phase difference) between area sensor parts. The detecting device can be used, for example, in another camera except the SLR camera in order to measure a distance from a photographic subject using each positions of the area sensor parts, based on principle of triangulation. The area photo acceptance units, which are of the charge accumulation type, are, for example, solid-state image sensing devices.
In the detecting device, the at least one of brightness monitoring photo acceptance units, arranged on the center of detecting area of at least one of the area photo acceptance units, can monitor the brightness of the central part and its neighborhood in the detection area. Thus, the detecting devices can make the detecting error reduced. Specifically, main photographic subject, which focus or a distance from which should be detected by the detecting device, is usually arranged, for example, at the central position in the detecting region and can be monitored by the brightness monitoring photo acceptance units. While conventional devices, in which the brightness monitor is arranged around the detecting region, monitor the brightness not of the central position in the detecting region but of the peripheral position therein, and then sometime have large detecting errors for the main photographic subject.
Thus, the above-mentioned detecting device can make the detecting error reduced even in the case that the brightness distribution of the subject is not uniform.
In order to achieve the other of the above objects, according to another aspect of the present invention, there is provided a camera having a detecting device for detecting one of a focusing condition of a taking lens and a distance from a subject to be photographed, said camera comprising: optical members which form respective subject images on respectively individual positions; area photo acceptance units, which are of a charge accumulation type, arranged on the respectively individual positions focused by the optical members; and at least one of brightness monitoring photo acceptance units, arranged across a detecting area of at least one of the area photo acceptance units, for controlling charge accumulating time of the area photo acceptance units.